What attracts birds to newly mown pasture? Decoupling the action of mowing from the provision of short swards

Many bird species flock to forage on newly mown grass swards. Several potential benefits are offered by such swards, including increases in prey availability (flush of foliar prey, reduced physical obstruction to surface and soil prey) and a foraging environment with fewer visual obstructions, so allowing predators to be detected more easily. We performed a field experiment using captive Common Starlings Sturnus vulgaris foraging in bottomless enclosures on newly mown swards (within 1 h) and old mown swards (48 h). We performed the experiment during winter months and standardized sward height to exclude other confounding effects in order to determine the temporal benefits of mowing for species foraging on soil invertebrates. We found no differences in the vigilance or time budgets of Starlings foraging on newly or old mown swards. Intake efficiency (prey captured per 100 roots) was greater on newly mown swards, suggesting that Starlings used less energy to obtain their prey on that substrate. It is possible that mowing alters the microclimate of the soil and sward, causing invertebrate availability to decline over time, which causes the lower foraging efficiency. Mowing is a technique often used to manipulate grassland habitats in ecological research; it has recently been advocated as a conservation management tool for wintering bird populations. We suggest that care should be taken when designing such studies to avoid confounding the factors under investigation with temporal changes in prey availability.     

Habitat affects escape behaviour and alarm calling in Common Starlings Sturnus vulgaris

Animals should adapt their escape behaviour to both physical and social surroundings in order to maximize their probability of survival. Cover can be both obstructive, reducing the visibility of the surroundings and hindering escape, and protective, providing refuge. We investigated how the provision of cover (long grass) affected (1) the escape behaviour and (2) the alarm call behaviour of Common Starlings Sturnus vulgaris responding to a model hawk during a simulated attack. Starlings always retreated away from the predator and sometimes alarm-called. Their escape trajectory was close to the ground when escaping in long grass, which could be explained by either tall swards hindering take-off or such swards being used as protective cover. On short grass their escape trajectory was much steeper (> 45°). We also investigated the use of alarm calls in Starlings according to predictions arising from the costs and benefits to callers and receivers. Callers could benefit from using alarm calls through dilution or confusion if their use initiates flock departures, thus reducing their probability of being targeted. If there is no cost to the producer of alarm calls we predicted that detectors should call at all times to gain these benefits (i.e. irrespective of grass length), but if their use is costly we predicted that they would be used only when the benefits outstrip the costs. In this case we would predict that alarm calls would be given when other (visual) signals were impaired on long grass but not when they were effective on short grass. Starlings used alarm calls on long grass when visibility was reduced more frequently than on short grass, suggesting that calling has a cost to the producer. The contrasting escape strategies of Starlings in relation to a relatively small (10 cm) change in grass height demonstrates the potential importance of habitat structure in determining predation risk.     

Polymorphic microsatellite loci from the West Nile virus vector Culex tarsalis

Since its introduction in 1999, West Nile virus (WNV) has spread across North America. Culex tarsalis is a highly efficient WNV vector species. Many traits such as virus susceptibility, autogeny and host preference vary geographically and temporally in C. tarsalis. Culex tarsalis genomic libraries were developed and were highly enriched for microsatellite inserts (42–96%). We identified 12 loci that were polymorphic in wild C. tarsalis populations. These microsatellites are the first DNA‐based genetic markers developed for C. tarsalis and will be useful for investigating population structure and constructing genetic maps in this mosquito.     

Photoperiodic effects on post-weaning growth and food consumption in the collared lemming Dicrostonyx groenlandicus

The effects of long 'summer' (22L:2D) and short 'winter' (2L:22D) photoperiod on post-weaning growth and food consumption of the collared lemming were examined. Growth was described by Gompertz equations. After 10 weeks, lemmings maintained under short photoperiods developed white winter pelage and heavy bifid claws; body mass and estimated asymptotic mass were significantly greater than for lemmings reared under long photoperiod. Sexual dimorphism in body size was observed within treatments, males growing larger than females. There were no significant differences in the overall growth rate constant k as a result of either sex or photoperiod treatment. However, instantaneous growth rates (dW/dt) were significantly higher in 'winter' lemmings. Mass at weaning was a significant determinant of adult mass at 90 days.
Cumulative food consumption at 90 days was not significantly different between photoperiod groups, even though 'winter' lemmings gained more than double the mass of their 'summer' counterparts over the post-weaning period. Increased gut length observed for winter morphs may act as the physiological mechanism promoting greater gross energy efficiency.
The present study suggests that the overwintering strategy of the collared lemming with respect to body mass changes and energy requirements differs considerably from that of other microtines.     

High-Speed Cell Sorting of Infectious Trophic and Cystic Forms of Pneumocystis carinii

ABSTRACT. The separation of Pneumocystis carinii life-cycle stages while preserving infectivity is a hitherto unresolved challenge. We describe an original, reproducible, and efficient method for separating trophic from cystic forms of P. carinii using a high-speed cell sorter. The large amounts of highly purified (99.6±0.3%) infectious trophic and cystic forms can now be used to elucidate the poorly understood P. carinii life cycle.     

Quantitative criteria for species delimitation

Species are the fundamental units of biology, ecology and conservation, and progress in these fields is therefore hampered by widespread taxonomic bias and uncertainty. Numerous operational techniques based on molecular or phenotypic data have been designed to overcome this problem, yet existing procedures remain subjective or inconsistent, particularly when applying the biological species concept. We address this issue by developing quantitative methods for a classic technique in systematic zoology, namely the use of divergence between undisputed sympatric species as a yardstick for assessing the taxonomic status of allopatric forms. We calculated mean levels of differentiation in multiple phenotypic characters – including biometrics, plumage and voice – for 58 sympatric or parapatric species‐pairs from 29 avian families. We then used estimates of mean divergence to develop criteria for species delimitation based on data‐driven thresholds. Preliminary tests show that these criteria result in relatively few changes to avian taxonomy in Europe, yet are capable of extensive reassignment of species limits in poorly known tropical regions. While we recognize that species limits are in many cases inherently arbitrary, we argue that our system can be applied to the global avifauna to deliver taxonomic decisions with a high level of objectivity, consistency and transparency.     

Spatial variation in the magnitude and functional form of density‐dependent processes on the large skipper butterfly Ochlodes sylvanus

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The circadian clock‐associated gene gigantea1 affects maize developmental transitions

The circadian clock is an internal timing mechanism that allows plants to make developmental decisions in accordance with environmental conditions. In model plants, circadian clock‐associated gigantea (gi) genes are directly involved in control of growth and developmental transitions. The maize gigantea1 (gi1) gene is the more highly expressed of the two gi homeologs, and its function is uncharacterized. To understand the role of gi1 in the regulatory networks of the maize circadian clock system, gi1 mutants were evaluated for changes in flowering time, phase change and growth control. When grown in long‐day (LD) photoperiods, gi1 mutants flowered earlier than non‐mutant plants, but this difference was not apparent in short‐day (SD) photoperiods. Therefore, gi1 participates in a pathway that suppresses flowering in LD photoperiods, but not in SD. Part of the underlying cause of early flowering was up‐regulated expression of the FT‐like floral activator gene zea mays centroradialis8 (zcn8) and the CONSTANS‐like flowering regulatory gene constans of zea mays1 (conz1). gi1 mutants also underwent vegetative phase change earlier and grew taller than non‐mutant plants. These findings indicate gi1 has a repressive function in multiple regulatory pathways that govern maize growth and development.     

Extraordinary web and silk properties of Cyrtarachne (Araneae, Araneidae): a possible link between orb-webs and bolas

Cyrtarachne is an orb-weaving spider of the sub-family Cyrtarachninae (Araneidae), which includes the triangle-web-building Pasilobus and the bolas spiders. We found that web and thread characteristics of Cyrtarachne differed greatly from those of typical orb-webs. Web diameter, sticky spiral spacing, breaking strength and stickiness of thread, thread diameter and droplet diameter were significantly different from those of other members of Araneidae. It is especially worth noting that the diameter was approximately four times, and the breaking strength seven to ten times larger in Cyrtarachne viscid threads than in those of other araneids. Kinetic energy-absorbing ability of Cyrtarachne threads was much greater than in that of other species, and close to the amount of kinetic energy generated by flying moths. Viscid material of threads was peculiar because its adhesiveness decreased to zero in a few hours. Moreover, SEM photos revealed them to be covered with thin scales of material, while threads of other araneids were smooth. These two facts suggest that the viscid material of Cyrtarachne threads may be different from those of other orb-weavers. As web-building, hunting behaviour and prey composition of different species of Cyrtarachninae arc quite similar to each other, we hypothesize that these extraordinary web and thread characteristics of Cyrtarachne are shared by the other members of this sub-family. Because these characteristics differ in many ways from those of typical araneid orb-webs, there appears to have been a great leap in evolution between Cyrtarachne and the other Araneidae.